1. Field of the Invention
The present invention relates to crosslinked polymeric microparticles, their method of preparation and to their use in coating compositions.
2. Brief Description of the Prior Art
Crosslinked polymeric microparticles of various types are known in the prior art and offer a way of obtaining high solids compositions for use in coating applications. An advantage of using crosslinked polymeric microparticles in coatings is that they make possible a higher solids content than would otherwise be possible without causing an increase in viscosity. In addition, the crosslinked polymeric microparticles improve pigment orientation. For example, when aluminum flakes or metal oxide coated micas are present in the coating compositions, the crosslinked polymeric microparticles make the aluminum flakes and the metal oxide coated micas which have flake-like dimensions lie flat which is very difficult to do in high solids systems. Additionally, it has been found that the crosslinked polymeric microparticles give a high level of sag resistance in high solids coating compositions permitting the application of thicker coatings.
Crosslinked polymeric microparticles have been prepared by non-aqueous dispersion polymerization techniques. However, these procedures required the use of specific organic solvents, specific monomers and specific reaction sequences so as to prepare the crosslinked polymeric microparticles in a stably dispersed manner.
The prior art also discloses that the crosslinked polymeric microparticles can be prepared in aqueous medium. A description of prior art in this area is presented below.